From: Pavel Machek <pavel@ucw.cz>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Linux Kernel Developers List <linux-kernel@vger.kernel.org>,
linux-crypto@vger.kernel.org, smueller@chronox.de,
herbert@gondor.apana.org.au, andi@firstfloor.org,
sandyinchina@gmail.com, jsd@av8n.com, hpa@zytor.com
Subject: Re: [PATCH 7/7] random: add backtracking protection to the CRNG
Date: Sun, 26 Jun 2016 20:47:53 +0200 [thread overview]
Message-ID: <20160626184753.GB11162@amd> (raw)
In-Reply-To: <1465832919-11316-8-git-send-email-tytso@mit.edu>
On Mon 2016-06-13 11:48:39, Theodore Ts'o wrote:
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
> drivers/char/random.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 49 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index d640865..963a6a9 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -436,7 +436,8 @@ static int crng_init = 0;
> #define crng_ready() (likely(crng_init > 0))
> static void _extract_crng(struct crng_state *crng,
> __u8 out[CHACHA20_BLOCK_SIZE]);
> -static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]);
> +static void _crng_backtrack_protect(struct crng_state *crng,
> + __u8 tmp[CHACHA20_BLOCK_SIZE], int used);
> static void process_random_ready_list(void);
You can do u8 and u32 in the code, we know we are in kernel.
> +/*
> + * Use the leftover bytes from the CRNG block output (if there is
> + * enough) to mutate the CRNG key to provide backtracking protection.
> + */
> +static void _crng_backtrack_protect(struct crng_state *crng,
> + __u8 tmp[CHACHA20_BLOCK_SIZE], int used)
> +{
> + unsigned long flags;
> + __u32 *s, *d;
> + int i;
> +
> + used = round_up(used, sizeof(__u32));
> + if (used + CHACHA20_KEY_SIZE > CHACHA20_BLOCK_SIZE) {
> + extract_crng(tmp);
> + used = 0;
> + }
> + spin_lock_irqsave(&crng->lock, flags);
> + s = (__u32 *) &tmp[used];
> + d = &crng->state[4];
> + for (i=0; i < 8; i++)
> + *d++ ^= *s++;
> + spin_unlock_irqrestore(&crng->lock, flags);
> +}
You are basically trying to turn CRNG into one way hash function here,
right? Do you have any explanation that it has the required
properties?
Thanks,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
next prev parent reply other threads:[~2016-06-26 18:47 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-13 15:48 [PATCH-v4 0/7] random: replace urandom pool with a CRNG Theodore Ts'o
2016-06-13 15:48 ` [PATCH 1/7] random: initialize the non-blocking pool via add_hwgenerator_randomness() Theodore Ts'o
2016-06-13 15:48 ` [PATCH 2/7] random: print a warning for the first ten uninitialized random users Theodore Ts'o
2016-06-13 15:48 ` [PATCH 3/7] random: add interrupt callback to VMBus IRQ handler Theodore Ts'o
2016-06-13 15:48 ` [PATCH 4/7] random: properly align get_random_int_hash Theodore Ts'o
2016-06-13 15:48 ` [PATCH 5/7] random: replace non-blocking pool with a Chacha20-based CRNG Theodore Ts'o
2016-06-13 18:00 ` Stephan Mueller
2016-06-13 19:03 ` Theodore Ts'o
2016-06-15 14:59 ` Herbert Xu
2016-06-19 23:18 ` Theodore Ts'o
2016-06-20 1:25 ` Herbert Xu
2016-06-20 5:02 ` Theodore Ts'o
2016-06-20 5:19 ` Herbert Xu
2016-06-20 15:01 ` Theodore Ts'o
2016-06-20 15:49 ` Stephan Mueller
2016-06-20 18:52 ` H. Peter Anvin
2016-06-20 23:48 ` Theodore Ts'o
2016-06-26 18:47 ` Pavel Machek
2016-06-26 19:10 ` Stephan Mueller
2016-06-26 22:51 ` Theodore Ts'o
2016-06-13 15:48 ` [PATCH 6/7] random: make /dev/urandom scalable for silly userspace programs Theodore Ts'o
2016-08-21 9:53 ` Jan Varho
2016-08-21 11:36 ` Theodore Ts'o
2016-06-13 15:48 ` [PATCH 7/7] random: add backtracking protection to the CRNG Theodore Ts'o
2016-06-26 18:47 ` Pavel Machek [this message]
2016-06-26 23:05 ` Theodore Ts'o
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